1. Field of Invention
The present invention relates to a motor vehicle lock, and, more specifically to a motor vehicle door lock for a trunk lid or a tailgate of a motor vehicle.
2. Description of Related Art
Known motor vehicle locks, designed and suitable for a trunk lid or the tailgate of a motor vehicle as described in German Patent Application DE 195 05 779 A1 (which corresponds to U.S. Pat. No. 5,938,253) are advantageous because an electric motor drive can be controlled without a reset spring by a driving element which rotates in one rotational direction in blocking operation, and thus, without microswitches.
The known motor vehicle lock noted above is made such that, when the electric motor drive fails, emergency actuation by hand enables the ratchet to be moved, at any time, into the lifted position. Overall, for the mechanical background of motor vehicle locks of the type under consideration, and for the particulars in motor vehicle locks for trunk lids or tailgates, reference should be made to U.S. Pat. No. 5,938,253, the contents of which are incorporated by reference in their entirety.
In the above-described known motor vehicle lock, a driver element is described as a cylindrical component. For the purposes of this application, however, a crank-like component or a component with some other shape, such as an elliptical shape, can also be regarded as the driver element. As in the prior art, the drive is provided with a degressive starting characteristic. This means that, upon starting, a large torque can be applied in order to release the ratchet from the engagement position on the latch. As the lifting motion of the ratchet continues, this torque is continuously reduced by the shape of the driver element. In particular, a control crank in the shape of a helical cam as a driver element has come into use as shown in German Patent Application DE 101 00 008 A1 (which corresponds to U.S. Pat. No. 6,698,805). In this respect, implementation of stepped reduction of the torque by lever action arms of different length is also known as shown in German Patent DE 41 19 703 C1. This is not implemented with the driving element of an electric motor drive in which the driving element rotates in one direction. However, in a motor vehicle lock with manual actuation, it is implemented via a gradually acting coupling of the opening handle to the ratchet.